1. Field of the Invention
The present invention relates to a method for manufacturing a memory. More particularly, the present invention relates to a method for manufacturing a memory with uniform thickness of the floating gate dielectric layer.
2. Description of the Prior Art
Flash memory is widely used because of its capability of non-volatile information storage. Generally speaking, flash memory is divided into two groups, NOR flash memory and NAND flash memory.
In NAND flash memory, the thickness of the floating gate dielectric layer plays an important role. FIG. 1 illustrates a conventional memory cell of NAND flash memory. The memory cell 100 includes a substrate 110, a floating gate 120, a floating gate dielectric layer 121, a control gate 130 and a control gate dielectric layer 131. The floating gate dielectric layer 121 is disposed between the substrate 110 and the floating gate 120, and the dielectric sidewall 140 is disposed between the floating gate 120 and the control gate 130.
In the conventional production of NAND flash memory, usually first the floating gate dielectric layer 121 then the control gate dielectric layer 131 is formed. When the floating gate dielectric layer 121 is formed, the thickness of the floating gate dielectric layer 121 can be well controlled. In other words, the thickness around the center of the floating gate dielectric layer 121 (a) and the thickness around both sides (b) are about the same.
However, after the control gate dielectric layer 131 is formed, the thickness of b would be increased due to the bird's beak of the control gate dielectric layer 131. The b point would have the best writing effect because of the strongest electric field, but now the total performance of the flash memory is drastically diminished due to the worse writing effect caused by the bird's beak.
Accordingly, a novel method for manufacturing a memory is needed to control the evenness of the thickness of the floating gate dielectric layer.